The Revised 24-Hour
PM-2.5 Standard and Compliance Deadlines

OnFebruary 24, 2009, as a result
of the suit filed against the U.S. EPA
by public health and environmental groups, the U.S. Court of Appeals for
the D.C. Circuit remanded the National Ambient Air Quality Standards
(NAAQS) for fine particulate matter (PM2.5) to EPA for reconsideration
of the annual level of the standard (which EPA left at 15 micrograms
per cubic meter (µg/m3)) and reconsideration of the secondary
PM2.5 NAAQS. With respect to the annual PM2.5 NAAQS, the court
held that the agency failed to explain adequately why an
annual level of 15 µg/m3 is requisite to protect
the public health, including the health of vulnerable subpopulations,
while providing an adequate margin of safety. 42
U.S.C.§ 7409(b)(1). For the secondary standards, the
court held that EPA unreasonably concluded that the NAAQS
are adequate to protect the public welfare from adverse effects
on visibility. The court denied petitions for review of
the primary daily standard for coarse PM and the petition for
review of EPAs revocation of the primary annual standard
for coarse PM. The Court opinion can be read by clicking
here.

On
September 21, 2006, EPA announced with regard to primary standards
for fine particles (generally referring to particles less than
or equal to 2.5 micrometers (µm) in diameter, PM-2.5) that
it was revising the level of the 24-hour PM-2.5 standard to 35
micrograms per cubic meter (µg/m3) and retaining the level
of the annual PM-2.5 standard at 15 µg/m3. With regard
to primary standards for particles generally less than or equal
to 10 µm in diameter (PM-10), EPA retained the 24-hour
PM-10 and revoked the annual PM-10 standard. With regard to secondary
PM standards, EPA made them identical in all respects to the
primary PM standards, as revised. The issue of reliability of
the epidemiological time-series methodologies continues to be
of concern to the Administrator. The Administrator noted in his
decision that there were many sources of uncertainty and variability
inherent in the inputs to the assessment and that there was a
high degree of uncertainty in the resulting PM-2.5 risk estimates.
Such uncertainties generally related to a lack of clear understanding
of a number of important factors, including, for example, the
shape of concentration-response functions, particularly when,
as here, effect thresholds can neither be discerned nor determined
not to exist; issues related to selection of appropriate statistical
models for the analysis of the epidemiologic data; and the role
of potentially confounding and modifying factors in the concentration-response
relationships. For those interested in the violation areas for
the revised 24-hour PM-2.5 standard, please click here.

The 24-hour PM-2.5 compliance deadlines
are as follows:

10/17/06: PM NAAQS final rule published
in Federal Register.
12/18/06: Effective date of the final PM NAAQS rule.
12/18/07: Based on air monitoring data collected in 2004-2006,
States submit recommendations to EPA as to whether or not
local communities are complying with the PM NAAQS.
10/8/2009: EPA makes final PM compliance designations.
11/2009: Effective date for EPAs PM compliance designations.
11/2012: Deadline for States to submit PM State Implementation
Plans (SIP).
11/2014: Attainment date.
11/2019: Attainment date with extensions.